This invention relates to a non-catalytic process for reducing nitrogen oxide (NOx) emissions in the combustion effluent of a stationary combustion apparatus by contacting a nitrile compound with a waste stream, an auxiliary fuel stream, and air in the combustion zone of the combustion apparatus. In one aspect, this invention relates to a non-catalytic process for reducing NOx emissions in the combustion effluent of a stationary combustion apparatus by contacting a nitrile compound with an absorber off-gas (AOG) stream produced in a chemical plant, such as an acrylonitrile production process, an auxiliary fuel stream, and air in the combustion zone of the combustion apparatus.
As is well known, various oxides of nitrogen are produced during the combustion of most fuels with air. In general, these oxides result either from the oxidation of nitrogen in the air at the elevated temperatures of combustion or from the oxidation of nitrogen contained in the fuel. Such formation can occur in both catalytic and non-catalytic combustion although the formation is more predominant in non-catalytic combustion.
Various post-combustion technologies have been developed for reducing the concentration of NOx in combustion effluents. Post-combustion technologies have focused on non-selective gas phase NOx reduction, ammonia based selective catalytic reduction (SCR), and selective non-catalytic reduction (SNCR) using ammonia, urea, cyanuric acid, isocyanate, hydrazine, ammonium sulfate, atomic nitrogen, methyl amines, or bi-urates.
Other NOx reduction technologies include low NOx burners, air and fuel staging, flue gas recirculation, and catalytic scrubbing.
In Shelton, H. L., “Find the Right Low-NOx Solution”, Environmental Engineering World, November-December 1996, pp. 24-27, it is disclosed that burning fuel oil with nitrogen compounds or other non-conventional nitrogen-bearing fuels such as amines, HCN and other nitrile will increase NOx emissions. Shelton also discloses a complicated multi-stage thermal oxidizer for burning nitrites which feeds air, natural gas, a nitrogen-containing aqueous organic stream, and a liquid HCN stream to the burner section and then adds an absorber off-gas stream (low-oxygen, 400-600 ppm NOx) to the first oxidizing stage with the operating at 2300-2600° F. (1260-1427° C.). In a second reducing stage, which feeds additional absorber off-gas and operates at 1800° F. (982° C.), CN− radicals are disclosed to react with NOx producing CO as a byproduct. A third reoxidizing stage adds additional air and operates at 1600° F. (871° C.) to produce a stack gas having <200 ppm NOx.
SNCR technology which is commercially practiced uses ammonia and urea as reducing agents. However, a SNCR process which avoids the need for special mixing or injection hardware is desirable. It is also desirable to have a SNCR process which can use a lower temperature range than is typical in current commercial SNCR processes, such as ammonia SNCR, as lower temperature operation reduces fuel requirements in the combustion apparatus. It is also desirable to have a SNCR process which does not require a complicated multi-stage combustion apparatus. Surprisingly, a commercially practical process for reducing nitrogen oxide (NOx) emissions in the combustion effluent of a typical stationary combustion apparatus using a nitrile compound at lower temperatures than used in current SNCR processes has now been discovered.